First off, I am a clam cake junkie and will drive for hours to get a good fix. Reputedly, the very best clams (and fantastic seafood in general) in Mystic are found at the Sea Swirl clam shack, on the Stonington side of Route 1 in Mystic. It closes for the season in October, so after that you're stuck with the Cove, a bit further east on Route 1. Fried clam bellies - kinda small but not bad, wouldn't call them delicious and not even close to the top tier, but still quite tasty. Don't bother with the clam cakes. They're dry and tasteless. I actually ate two and threw the rest away, even knowing it would be many months before I could get back to southeastern CT or RI and get another fix.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.